The present invention relates to solvent resistant room temperature vulcanizable silicone rubber compositions and more particularly the present invention relates to a room temperature vulcanizable silicone rubber composition having fluorinated substituent groups in the polymers which are cured in the presence of a platinum catalyst to result in a solvent resistant elastomer.
Silicone elastomers are well known in the art and are desired for many applications in which high and low temperature stability are desired.
It is also known that silicone elastomers whether room temperature vulcanizable silicone elastomers or heat vulcanizable silicone elastomers have a certain amount of resistance to solvent degradation from hydrocarbon fluids. However, in certain applications, the solvent resistance to hydrocarbon fluids of traditional silicone elastomers has not been great enough. Accordingly, in an attempt to solve this problem, fluorinated substituted heat vulcanizable silicone rubber compositions were devised. See, for instance, the disclosure of U.S. Pat. Nos. 2,979,519 of Pierce et al and 3,179,619 of Brown. Such heat vulcanizable fluorinated substituted silicone rubber compositions as disclosed in the above patents have solvent resistance and the resulting elastomer has good physical properties for many applications.
However, one disadvantage of such heat vulcanizable silicone rubber compositions was that to obtain sufficient strength in the cured elastomer it was necessary to incorporate into it large amounts of filler and high molecular weight siloxane gums. Thus, the uncured composition of such heat vulcanizable silicone rubber compositions usually had a viscosity in the neighborhood of 50,000,000 centipoise and above at 25.degree. C. Accordingly, such a viscous, uncured composition is difficult to process and time consuming to produce fabricated parts from it such as, electrical connectors. This problem appears to be unresolvable with such compositions since the base diorganopolysiloxane gums that are used to prepare such heat vulcanizable silicone rubber compositions have a viscosity of anywhere from 1,000,000 to 200,000,000 centipoise at 25.degree. C. Accordingly, the resulting viscosity of the silica and gum mixture is bound to be at the level of 50,000,000 centipoise and above.
To solve this problem, some attempts have been made to produce a one-part room temperature vulcanizable silicone rubber composition. However, such compositions as is well known in the art have to be kept in an anhydrous state prior to cure. Accordingly, such compositions which have to be kept in an anhydrous state are also very difficult to process.
It was quite unexpected, therefore, that an SiH-olefin platinum catalyzed silicone rubber composition could be prepared having fluorinated substituent radicals such that the composition has the proper solvent resistance to hydrocarbon fluids, good physical properties and a fast cure rate at elevated temperatures. Such composition is, for instance, that disclosed in the copending application of Edward M. Jeram, Docket No. 60SI-51, filed on the same date as the present application entitled "Solvent Resistant Room Temperature Vulcanizable Silicone Rubber Compositions". However, the difficulty in such a composition is that it is desirable to incorporate fillers and specifically treated reinforcing fillers in the uncured composition so that the cured elastomer would have optimum physical properties. As a result, the viscosity of the uncured composition would be in the neighborhood of 4 to 6,000,000 centipoise at 25.degree. C., depending on how much filler was incorporated into the uncured composition.
Accordingly, it is desirable to have such an SiH-olefin platinum catalyzed silicone rubber composition which in the uncured state has substantially lower viscosity and in which various fillers may be incorporated into it, both extending and/or reinforcing fillers, without unduly increasing the viscosity of the final uncured composition.
It is one object of the present invention to provide for an SiH-olefin platinum catalyzed room temperature vulcanizable silicone rubber composition which has a very low viscosity in the uncured state and which in the cured state is solvent resistant, and which cures rapidly with no by-products when heated.
It is an additional object of the present invention to provide for an SiH-olefin platinum catalyzed silicone rubber composition which in the cured state has physical properties approaching or comparable to that of heat vulcanizable silicone rubber compositions but which does not necessitate the use of a filler.
It is yet an additional object of the present invention to provide for an SiH-olefin platinum catalyzed silicone rubber composition in which any type of filler may be incorporated into it such that the composition maintains its low viscosity in the uncured state and which in the cured state has desirable physical properties and is solvent resistant.
It is still another object of the present invention to provide a simple and economical process for preparing a solvent resistant SiH-olefin platinum catalyzed silicone rubber composition which has physical properties nearly comparable to that of heat vulcanizable silicone rubber compositions.
These and other objects of the present invention are accomplished by means of the disclosure set forth herein below.